1. Field of the Invention
The present invention relates to an apparatus and a method for transmitting and receiving an Automatic Repeat reQuest (ARQ) feedback message in a wireless communication system. More particularly, the present invention relates to an apparatus and a method for a receiving unit to transmit an ARQ feedback message without contention in a wireless communication system.
2. Description of the Related Art
According to a channel status of a radio resource, a wireless communication system can encounter an error in data transmitted and received. Hence, the wireless communication system controls or restores the data error using an Automatic Repeat reQuest (ARQ) scheme to raise transmission reliability.
Using the ARQ scheme, a receiving unit informs a transmitting unit of whether ARQ data is successfully received from the transmitting unit. For example, when the ARQ data received from the transmitting unit is free from an error, the receiving unit transmits ACKnowledge (ACK) information to the transmitting unit. When the ARQ data received from the transmitting unit is corrupted, the receiving unit transmits Negative ACK (NACK) information to the transmitting unit. Herein, a series of operations of the receiving unit for transmitting the reception success or failure of the ARQ data to the transmitting unit is referred to as an ARQ feedback.
Accordingly, the transmitting unit can acquire a reception status of the ARQ data transmitted to the receiving unit from the ACK/NACK information received from the receiving unit, and thus manages an ARQ window. When receiving the ACK information from the receiving unit, the transmitting unit updates the ARQ window and transmits new ARQ data to the receiving unit. In contrast, when receiving the NACK information from the receiving unit, the transmitting unit retransmits the ARQ data corresponding to the NACK information to the receiving unit without updating the ARQ window.
To transmit the ARQ feedback to the transmitting unit, the receiving unit needs an additional resource request, which may delay the ARQ feedback transmission. When the ARQ feedback transmission is delayed, the transmitting unit cannot additionally transmit the ARQ data, which adversely affects the entire system throughput. To avoid the delay of the ARQ feedback transmission, the transmitting unit transmits an ARQ feedback request message to the receiving unit and request the ARQ feedback in advance before the ARQ window is full. Despite of this request, severe contention and collision in the resource request for the ARQ feedback may increase the delay and adversely affect the entire system throughput.
A conventional method for the receiving unit to request the resource in the contention manner according to the ARQ feedback request message reception from the transmitting unit in the Institute of Electrical and Electronics Engineers (IEEE) standard 802.16e system is explained in five steps. When the transmitting unit transmits the ARQ feedback request message to the receiving unit, the receiving unit selects and transmits a random ranging code to the transmitting unit in step 1. Herein, the ranging code transmitted to the transmitting unit does not contain any information except for a code index. The transmitting unit allocates a resource for transmitting the resource request message to the receiving unit which transmits the ranging code, and transmits the corresponding resource allocation message to the receiving unit in step 2. If a plurality of receiving units transmits the ranging code at the same time, the ranging codes may collide and the ranging code transmission may fail. When the receiving unit does not receive the resource allocation message for the delivery of the resource request message after a certain time, the receiving unit repeats the selection and the transmission of a certain ranging code to the transmitting unit. The receiving unit, upon receiving the resource allocation message, transmits a resource request message including information such as an IDentifier (ID) of the receiving unit, a purpose of the resource request (to transmit the ARQ feedback) and a size of the requested resource, to the transmitting unit over the allocated resource in step 3. The transmitting unit receiving the resource request message allocates the resource for the ARQ feedback transmission to the receiving unit, and transmits a resource allocation message for the ARQ feedback transmission to the receiving unit in step 4. The receiving unit transmits the ARQ feedback to the transmitting unit over the allocated resource in step 5. That is, although an error does not occur during the five steps, the five steps are necessary for the ARQ feedback transmission. When an error occurs in the process of the five steps, the process from the first step should be repeated. As a result, the delay of the ARQ feedback transmission increases and blocks the ARQ data transmission of the transmitting unit.
Therefore, a need exists for an apparatus and method for reducing transmission delay of an ARQ feedback message in a wireless communication system.